There are various kinds of detecting sensors for using in currently commercially available car security systems. These sensors may be built in an antitheft main unit of the car security systems, or externally connected to the antitheft main units via wires. Most of the built-in sensors are designed to detect vibration and change of battery voltage of the cars. When any car door is opened, the car is vibrated, and a door light is on to result in minor change in the battery voltage of the car. Therefore, it is possible to detect an opened door through the change in battery voltage of the car. However, a chemical change in the battery or an automatic actuation of the cooling fan in a turbo car would also result in the change of battery voltage. Besides, a door light might not become on when the door is opened due to poor contact of the door light. In this case, the change of battery voltage due to an opened car door is very possibly lower than a preset triggering value and fails to trigger the car security system.
A sensor mounted outside the antitheft main unit may be a vibrating sensor, an ultrasonic sensor, or a microwave sensor. Ultrasonic and microwave sensors are used to detect any movement of any object in the car, and usually consume relatively high power. All these types of sensors have a common point, that is, they are connected to the main unit via wires, and the main unit can be easily located by a thief by tracing the wires.
There is developed a new type of steering wheel lock having a vibrating, an air pressure, or an infrared sensor built therein. The air pressure sensor is able to detect changes of air pressure in a car when a door is opened. The infrared sensor is used to detect changes of temperature in a car due to an invader. These types of sensors built in the steering wheel lock have the advantage of low power consumption. However, the steering wheel lock with the built-in sensor must be internally provided with batteries, which require frequent replacement to cause inconveniences to the user. And, it is embarrassing if the user fails to get new batteries when the old ones are exhausted. Alternatively, if it desired for the steering wheel lock with built-in sensor to be internally provided with chargeable batteries, a wire must be extended from the steering wheel lock to the cigarette-lighter socket to obtain power supply for charging the batteries. Therefore, it is inevitable to frequently plug and unplug the steering wheel lock into and from the cigarette-lighter socket. Moreover, it is uneasy to find a suitable place in the quite small interior of car to position the steering wheel lock, which has a considerably big volume, when the steering wheel lock is plugged in the cigarette-lighter socket and charged when the car is moving, particularly when the wire connecting the steering wheel lock to the cigarette-lighter socket is short. The wire extended from the steering wheel lock also tends to unexpectedly loosen from the cigarette-lighter socket and dangerously hinders the driver's feet.
There are also antitheft main units with the air pressure or the infrared sensor built therein. The main unit may be clipped to a flip-down sun visor or a dashboard, and is internally provided with general batteries to supply power needed by the main unit to operate normally. The batteries must be replaced now and then. When chargeable batteries are used to replace the general batteries, the user has to troublesomely connect a wire from a power source in the car to the main unit for charging the batteries.
It is therefore tried by the inventor to develop a method and apparatus for securing car against theft via wireless sensor to overcome the disadvantages existed in the conventional car security systems.